If you don't hear the rattle with the clutch depressed, but you do with it engaged, then I'd say that the noise is coming from the transmission.Happy Boxstering,Pedro

Pedro Bonilla
1998 Boxster 986 - 284,000+ miles: http://www.PedrosGarage.comPCA National Club Racing Scrutineer - PCA National HPDE Instructor - PCA Technical Committee (Boxster/Cayman)
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QuoteLew
I have been experiencing a rattling noise when I turn off the engine.....I don't hear the rattling noise when turning off the engine with the clutch pressed in. Is the Dual Mass Flywheel bad?

Probably not the DMF. (But it can't be eliminated entirely. See below.) When bad they clunk when taking off and sometimes when shifting.

The fact the noise is not present when you turn off the engine with the clutch pedal depressed and the clutch disengaged suggests to me the noise is coming from the transmission. In this case the transmission is disconnected from the engine.

If the clutch pedal is not depressed, as the engine stops running the engine's rotation becomes more erratic and the normal transmission shaft spline and gear fits/clearances lets some transmission hardware rattle.

As an aside, the DMF also acts as a vibration dampener. That it appears it is not effective in this regard could be the early signs of a going bad DMF.

Never heard this noise with my Boxster but when the Turbo transmission was up to temperature with the engine just idling the transmission would rattle a bit. I knew it was the transmission because the noise stopped when I disengaged the clutch.

Might add that at some point: when I had new plugs and coils installed or at another time new O2 sensors installed; the Turbo transmission rattle was gone. My theory is the rattle was from the engine running a bit "rough" and needing a "tune up". Th engine never misfired even under hard acceleration but I do recall after new plugs and coils and then again after new O2 sensors the engine ran noticeably better.

In the case of your car you can check or have checked the engine and transmission mounts.

If it hasn't been done recently consider having the transmission/diff fluid changed. I had this done to both my cars and I just let the dealer do it and use the factory fluid.

Also, if it hasn't been done recently have the brake and clutch fluid flushed and bled. This should be done every 2 years. My experience is letting this fluid service go even after just 2.5 years the fluid can deteriorate to the point the clutch hydraulic system is affected.

Thanks for the reply. I am up for the changing the brake fluid next month. I did it myself 2 years ago....My PBS only has 33k miles on it. The Transmission fluid change is on the list. Again thanks for your input. As said earlier the car runs and shifts great and there is no noise at anytime when driving. Just when I stop and shut down the engine I hear the rattle. Not sure how serious this is, but I plan on keeping the clutch depressed when turning off the engine. I think changing the transmission fluid might help and it might even be a little low. Will check ASAP. I do all the wrenching on my cars, and have only one fault code on the Boxster now which is a code 34 the passenger side motion sensor. I never have had a CEL on the Boxster. .

You have to do more than just change the brake fluid you need to after you have gone around the car in the proper sequence and flushed/bled every caliper then you need to flush/bleed the clutch slave cylinder.

Without being able to hear the noise -- and this is not a subtle or not so subtle hint to provide one -- it is impossible to make any judgement call about the severity or urgency of the noise, what may be at its root cause. My advice is you have this checked out by a qualified Porsche tech, get his opinion.

33K miles is not a lot of miles. There is AFAIK no requirement to change/replace the transmission fluid based on time. 'course, I'm a fan of early/more aggressive fluid change schedules and I'm OK with an early fluid change to see if it has any positive effect on the noise. For my 2002 Boxster the shop time to replace the 5-speed transmission fluid was just 0.3 hours. While the fluid is a bit pricey it is not like one is having to buy this all the time. The transmission fluid service for my Boxster was the least expensive service.

Assuming no leak or a prior improper fluid service that left the level low and these transmissions do not "use" oil/transmission fluid, so what makes you think the transmission fluid is low? Certainly if the fluid level is low there is less fluid to act as a dampener and to keep the the transmission internals from rattling around.

If the fluid is low this needs to be addressed and just as important the reason why it is low needs to be addressed.

QuoteMarcW
You have to do more than just change the brake fluid you need to after you have gone around the car in the proper sequence and flushed/bled every caliper then you need to flush/bleed the clutch slave cylinder.

I understand on what all you have to do when changing the brake fluid. Each caliper in the proper sequence was bled using my vacuum pump, and the slave cylinder for the clutch was also bled.

Without being able to hear the noise -- and this is not a subtle or not so subtle hint to provide one -- it is impossible to make any judgement call about the severity or urgency of the noise, what may be at its root cause. My advice is you have this checked out by a qualified Porsche tech, get his opinion.

I talked to a Porsche Tech and he sees where a spring or springs on the DMF jumps off and causing this type of rattle. He will be seeing the car today

33K miles is not a lot of miles. There is AFAIK no requirement to change/replace the transmission fluid based on time. 'course, I'm a fan of early/more aggressive fluidchange schedules and I'm OK with an early fluid change to see if it has any positive effect on the noise. For my 2002 Boxster the shop time to replace the 5-speed transmission fluid was just 0.3 hours. While the fluid is a bit pricey it is not like one is having to buy this all the time. The transmission fluid service for my Boxster was the least expensive service.

My 04 since new has had the oil changed along with a new filter every 5k miles. It also has been kept in a climate controlled atmosphere since new. I recently did the 30k maintenance. Plugs, all the Filters, drive belt. and fresh engine oil. However I have never changed the Transmission fluid. My brake pads and disc are like new and never been changed. I might add I never abuse my car, but enjoy it's willingness to do what I what it to do. It does get a lot of TLC. At 59k new, it looks new today.

Assuming no leak or a prior improper fluid service that left the level low and these transmissions do not "use" oil/transmission fluid, so what makes you think the transmission fluid is low? Certainly if the fluid level is low there is less fluid to act as a dampener and to keep the the transmission internals from rattling around.

I feel certain the fluid level is OK in the transmission. However I plan on changing it myself ASAP. My 6 speed gets new oil until it flows back from the opening. Your 5 speed is a little different.

If the fluid is low this needs to be addressed and just as important the reason why it is low needs to be addressed.

I just cannot believe this rattle is the DMF, or Transmission. The other day after starting the engine, and the car sat in the garage for a few minutes, I started to back out with the engine at idle rpm's around 6 to 7 hundred. When slowly letting out the clutch I hear this rattle. At that engine speed is when things may vibrate, thus rattles might be heard. I don't hear this noise backing up with the engine up to temperature. My thoughts are, it's the darn muffler. I have rubber hammered on it several times but don't hear or see anything loose. Dr. Know around?

My 2002 manifested a low frequency dull knocking noise when started cold. After the engine was up to temperature the noise was an irritating high pitched buzzing noise.

The knocking noise had me at one point thinking serious internal engine problems like a rod bearing or too much end play in the crankshaft. The buzzing noise had be believing (hoping) it was from a heat shield.

Turned out to be a converter brick was loose. (Suspect this got broken some years earlier from a piece of concrete that I ran over and which hit the exhaust manifold -- left a gouge in the metal.)

Cold the loose brick knocked about and hot it buzzed. Bought 2 used exhaust/converter manifolds -- shook the heck out of them to be sure there was nothing loose inside or falling apart inside -- and had them installed. Ahhhh. Quiet again and all was right with the world. And an intermittent CEL with a P0420 error code was gone too.

Don't be banging on the exhaust too hard, even with a rubber hammer. With everything cold and the car in the air -- you might have to arrange to leave the car at the shop and on the lift overnight so it is cold and you have good access to the exhaust -- all the exhaust pipes need to be checked for any excessive play, looseness. Visually check all the exhaust hangers. See where they attach to the car and the exhaust they are secure. A weld can break and the hanger looks like it is right up against the exhaust and everything is good but with some effort you can move the hanger about when you shouldn't otherwise be able to.

With a good flashlight and a mirror on a stick/swivel run along exhaust exhaust manifold from head to tip checking for something laying against the exhaust or even just close to the exhaust. Mainly you are concerned with something above or to one side of the exhaust. As the engine encounter load it moves some and if it moves enough to touch against something you can get a noise.

Thanks Andrew, I have used my rubber hammer rapping on the exhaust system from the oxygen sensors back to the exhaust tips. The heat shields seem not to be a problem, and both are tight. There are shields on the exhaust pipes before the cats, and they too seem tight and not rattling. Someone mentioned theirs rusted and became loose causing a annoying rattle. I have been thinking about removing the rear bumper and the muffler. That should help in narrowing down the problem.

Well, yesterday I was in a quiet place with the drivers door open and slowly backing up with engine at idle speed listening for this rattle. After several times both moving forward and backward at idle speed, I stalled the engine in reverse, which we all know how that sounds. Clunk! After restarting the engine, and moving forward slowly I could hear rattling that continued until I stopped, and rattling moving in reverse until I stopped. However there was no rattling heard when stopped with the clutch in or out. This rattle continued for a few minutes moving slowly forward and backwards. After a few minutes sitting still I moved away and did not hear the rattle.

If the rattling noise is only present when the car is moving that can be something loose with the exhaust but it also raises the possibility of a bad CV bearing, loose/damaged brake pads, to name two things that come to mind before I've had my morning coffee.

You might (might) eliminate the brake hardware by testing if you can affect the noise by lightly applying the brakes when the noise is present.

For the CV joint an inspection of the boots and a check for excessive play at each joint is called for. Generally boots go bad but the CV joint can be resurrected with cleaning and repacking with grease if an inspection turns up no reason to replace the joint. But a CV joint failure -- at least the presence of noise which suggests failure or failure is imminent -- can have a perfectly fine boot.

The car should be lifted in the air and by its tires/wheels so the half shafts are relatively unloaded. If you lift by the body lift points the suspension sags and the half shafts droop and even this load can mask looseness.

I recently spoke to a Porsche Tech at a Dealership while picking up a part about the rattle I was experiencing. The DMF was mentioned, clutch in switch off, no rattle, clutch out switch off the rattle. No mention of the Transmission. He ruled out the DMF. The tech said it could be a rusty release bearing. Anyone ever have a rusty throw out bearing making a noise?.

QuoteLew
I recently spoke to a Porsche Tech at a Dealership while picking up a part about the rattle I was experiencing. The DMF was mentioned, clutch in switch off, no rattle, clutch out switch off the rattle. No mention of the Transmission. He ruled out the DMF. The tech said it could be a rusty release bearing. Anyone ever have a rusty throw out bearing making a noise?.

Rust is not a common problem with throw out/release bearings in my nearly 50 years of experience with a number of different cars equipped with a manual transmission.

The only throw out bearing problem I experienced was when the one in my '96 Mustang GT got noisy. It was fine every time I used the clutch until it wasn't. When I pressed on the clutch pedal what proved to be the throw out bearing made a horrible screeching noise.

'course, just because I never experienced this problem directly or learned of it 2nd (even 3rd) hand doesn't mean it is not at least possible in your case.

Still, a transmission out job is a big undertaking with no more than a suspected "rusty" release bearing as the only reason to drop the transmission.

I'm thinking you need to find a place that can with a very high degree of confidence diagnose the source of the noise. While I and others can throw out (no pun...) ideas/suggestions at some point someone's got to get his hands dirty and really check the car over and locate/pin point the source of the noise. Your job is to be able to clearly detail the circumstances under which the noise appears and does not appear and to be able to help the tech reproduce the noise.